Fault current limiter with modular mutual reactor

ABSTRACT

Embodiments of the disclosure include a fault current limiter having a first current splitting device including a primary winding and secondary winding wound around a first core, and a second current splitting device including a primary winding and a secondary winding wound around a second core. The fault current limiter may further include a fault current limiter module (e.g., a switching module) electrically connected in series between the secondary winding of the first current splitting device and the secondary winding of the second current splitting device. The fault current limiter may further include a second fault current limiter module electrically connected in series with the secondary winding of the second current splitting device. By splitting the fault current limiter into parts with fault current limiter modules interspersed between the windings, the fault current limiter may be to be built with less insulation between the windings.

FIELD

This disclosure relates to fault current limiters, and more particularlyto a fault current limiter system having a fault current limiterswitching module interspersed between windings.

BACKGROUND

A fault current limiter (FCL) is a device for limiting fault currents,such as in a power system. Various types of FCLs have been developedover the last several decades, including superconducting fault currentlimiters (SCFCLs), solid state fault current limiters, inductive faultcurrent limiters, as well as other varieties known in the art. The FCLmay be implemented in a system having generation, transmission, anddistribution networks for providing power to various industrial,commercial, and/or residential electrical loads.

A fault current is an abnormal current in an electrical system resultingfrom a fault in the system, such as a short circuit. A fault current mayarise in a system due to any number of events or failures, such as powerlines or other system components being damaged by severe weather (e.g.lightning strikes). When such a fault occurs, a large current (a faultcurrent) can quickly appear in the circuit as the current is no-longerlimited by load. This surge of current is undesirable because ofpotential damage to the load, including the network itself, or equipmentconnected to the network.

Some prior art fault current limiters include a current splittingreactor having interleaved windings, wherein the current splittingreactor includes a core, a first winding wound around the core, and asecond winding wound around the core and interleaved with the firstwinding to reduce an insertion impedance of the fault current limiter.Lower losses may be achieved by interleaving primary and secondarywindings. Prior art fault current limiters built as a combined reactormay suffer from a build-up of inter-winding voltage. As the voltageincreases, the necessary insulation at the points of interleavingcorrespondingly increases, thus making the fault current limiter bulkyand making flux cancelation more difficult to achieve.

With respect to these and other considerations the present disclosure isprovided.

BRIEF SUMMARY

A fault current limiter according to an embodiment of the presentdisclosure includes a first current splitting device comprising aprimary winding and secondary winding wound around a first core, asecond current splitting device comprising a primary winding and asecondary winding wound around a second core. The fault current limiterfurther includes a fault current limiter module electrically connectedin series between the secondary winding of the first current splittingdevice and the secondary winding of the second current splitting device.

A power system according to an embodiment of the present disclosureincludes a power source, a load electrically connected to the powersource, a fault current limiter electrically coupled to the power sourceand the load to limit an amount of current during a fault condition. Thefault current limiter includes a first current splitting device having aprimary winding and secondary winding wound around a first core, asecond current splitting device comprising a primary winding and asecondary winding wound around a second core. The fault current limiterfurther includes a fault current limiter module electrically connectedin series between the secondary winding of the first current splittingdevice and the secondary winding of the second current splitting device.

A fault current limiter according to an embodiment of the disclosureincludes a first current splitting device having a primary winding andsecondary winding wound around a first core, and a second currentsplitting device comprising a primary winding and a secondary windingwound around a second core. The fault current limiter may furtherinclude a first fault current limiter module electrically connected inseries between the secondary winding of the first current splittingdevice and the secondary winding of the second current splitting device,and a second fault current limiter module electrically connected inseries with the secondary winding of the second current splittingdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate exemplary approaches of thedisclosure, including the practical application of the principlesthereof, as follows:

FIG. 1 depicts a power system according to embodiments of thedisclosure;

FIG. 2 depicts an exemplary fault current limiter according toembodiments of the disclosure;

FIG. 3 depicts an exemplary fault current limiter module of the faultcurrent limiter of FIG. 2 according to embodiments of the disclosure;

FIG. 4 depicts the exemplary fault current limiter of FIG. 2 with closedends according to embodiments of the disclosure; and

FIG. 5 depicts an exemplary fault current limiter including multiplefault current limiter switching modules disposed between windingsaccording to embodiments of the disclosure.

The drawings are not necessarily to scale. The drawings are merelyrepresentations, not intended to portray specific parameters of thedisclosure. The drawings are intended to depict exemplary embodiments ofthe disclosure, and therefore are not be considered as limiting inscope. In the drawings, like numbering represents like elements.

DETAILED DESCRIPTION

The present embodiments will now be described more fully hereinafterwith reference to the accompanying drawings, where some embodiments areshown. The subject matter of the present disclosure may be embodied inmany different forms and are not to be construed as limited to theembodiments set forth herein. These embodiments are provided so thisdisclosure will be thorough and complete, and will fully convey thescope of the subject matter to those skilled in the art. In thedrawings, like numbers refer to like elements throughout.

As used herein, an element or operation recited in the singular andproceeded with the word “a” or “an” are understood as possibly includingplural elements or operations, except as otherwise indicated.Furthermore, references to “one embodiment” or “some embodiments” of thepresent disclosure may be interpreted as including the existence ofadditional embodiments also incorporating the recited features.

The present embodiments involve approaches for improved fault currentprotection. More specifically, various embodiments address issuesrelating to an increased voltage drop across windings in a currentsplitting device, and the corresponding increased insulation between thewindings. For example, by splitting the fault current limiter (FCL) intoparts with the FCL switching modules interspersed between windings ofthe current splitting device, the fault current limiter may be builtwith less insulation between the windings, thus making the task ofcancelling out the flux and therefore impedance, easier.

In some embodiments, a fault current limiter has a first currentsplitting device including a primary winding and secondary winding woundaround a first core, and a second current splitting device including aprimary winding and a secondary winding wound around a second core. Thefault current limiter may further include a fault current limiter module(e.g., a switching module) electrically connected in series between thesecondary winding of the first current splitting device and thesecondary winding of the second current splitting device. The faultcurrent limiter may further include a second fault current limitermodule electrically connected in series with the secondary winding ofthe second current splitting device. By splitting the fault currentlimiter into parts, with fault current limiter modules interspersedbetween the windings, the fault current limiter may advantageously be tobe built with less insulation between the windings.

Turning now to FIG. 1, an exemplary power system according toembodiments of the present disclosure will be described. As shown, thepower system 100, including a fault current limiter (FCL) 101, isimplemented to include generation, transmission, and distributionnetworks generating and delivering power to various industrial,commercial, and/or residential electrical loads. The FCL 101 may includea first current splitting device (CSD) 102 electrically coupled with afirst fault current limiter module (FCLM) 104, and a second currentspitting device (CSD) 106 electrically coupled with the CSD 102. The FCL101 may include a third CSD 107 in some embodiments. As shown, thesecond CSD 106 is further coupled to the first FCLM 104 and the thirdCSD 107, and with a second FCLM 108. In some embodiments, each of thefirst and second CSDs 102, 106 is a modular current splitting reactorhaving interleaved windings, as will be described in greater detailbelow.

As further shown, the power system 100 may be electrically connected inseries intermediate an AC power source 110 and one or more electricalloads 112 via conductors 115 and 117. One of ordinary skill in the artwill appreciate the FCL 101 can be implemented in a variety of otherapplications and power system configurations where fault currentlimiting is desirable. The particular power system 100 depicted in FIG.1 is therefore shown by way of example, and is not intended to belimiting.

Each of the first, second, and third CSDs 102, 106, 107 may have an opencore design. The FCL 101 including current splitting devices 102, 106,and 107, each having interleaved windings, advantageously provides lowinsertion impedance. As an example, the FCL 101 described herein mayhave insertion impedance during normal operating conditions resulting ina voltage dropped across the impedance, when carrying full load current,being less than 1% of the total system voltage.

The FCL 101 described herein may be implemented to limit fault currentsin any electrical system, such as, for example, transmission,distribution, and generation systems. Furthermore, in some cases, theCSDs 102, 106, 107 with interleaved windings may be implemented in asuperconducting FCL, a solid state FCL, a fast switch FCL, or ingeneral, any fault current limiting circuit configured to protect asystem from fault currents where low insertion impedance is intendedduring normal operation. In some examples, the FCL 101 may incorporatesaturated iron cores or shielded cores. In one non-limiting illustrativeexample, the FCL 101 with first and second CSDs 102, 106, 107 havinginterleaved windings as described herein, may be provided to lower theinsertion impedance of a saturated iron core FCL having a high insertionimpedance. Furthermore, various examples provided herein may beimplemented in FCL devices for high or low frequency systems.

Referring now to FIGS. 1-2, the FCL 101 will be described in greaterdetail. As shown, the first current splitting device 102 of the FCL 101may include a primary winding 114 and a secondary winding 116 woundaround a first core 118, such as an iron or air core. In one embodiment,the primary winding 114 and the secondary winding 116 may beconcentrically wound around an iron core referenced to the input (line)voltage and floated or insulated from earth and/or other CSD cores. Thesecond CSD 106 comprises a primary winding 120 and a secondary winding122 wound around a second core 125. The FCL 101 further includes thefirst FCLM 104 electrically connected in series between the secondarywinding 116 of the first CSD 102 and the secondary winding 122 of thesecond CSD 106. As shown, the windings of each of the first and secondCSDs 102, 106 are arranged in parallel with one another. Furthermore,the primary winding 114 of the first CSD 102 is electrically connectedin series with the primary winding 120 of the second CSD 106, forexample, along a path 124, and the primary winding 114 of the first CSD102 is electrically connected in parallel with the first FCLM 104. Insome embodiments, the primary winding 114 and the secondary winding 116wound around the first core 118 have a same or a different number ofturns. Similarly, the primary winding 120 and the secondary winding 122wound around the second core 125 have a same or a different number ofturns.

The FCL 101 may further include a third CSD 107 having a primary winding136 and a secondary winding 138 wound around a third core 140. Thesecond FCLM 108 is electrically connected in series between thesecondary winding 122 of the second CSD 106 and the secondary winding138 of the third CSD 107. As arranged, the first FCLM 104 and the secondFCLM 108 are electrically connected in series along a path 126.Furthermore, the primary winding 120 of the second CSD 106 iselectrically connected in series with the primary winding 114 of thefirst CSD 106 and the primary winding 136 of the third CSD 107, forexample, along a path 124. The primary winding 120 of the second CSD 106is also electrically connected in parallel with the first FCLM 104 andthe second FCLM 108. Each of the windings of the first, second, andthird CSDs 102, 106, 107 may be configured to exhibit minimal impedanceduring a steady state operation, and a comparatively larger impedance,for example, from the primary windings in series, when the secondarywindings are open circuited, such as during a fault condition, so as toeffectively limit the fault current.

In some embodiments, the FCL 101 may include a series of switches, suchas any fast opening technology, e.g., superconductor based, saturableiron core, mechanical or solid state switches with a voltage protectiondevice and a voltage control device. For example, as shown in FIG. 3,each of the first and second FCLMs 104, 108 may include a metal oxidevaristor (MOV) 150, a snubber 151, and a solid state switch 152 eacharranged in parallel with one another.

Referring now to FIGS. 2 and 4, operation of the FCL 101 will bedescribed in greater detail. In an exemplary embodiment, during a steadystate condition, the primary winding 114 and the secondary winding 116of the first CSD 102 may be set to distribute the steady state currentalong parallel paths 124 and 126 in a predefined manner. For example, ifx % of the steady state current flows along path 124, then the remainder(100−x) % of the steady state current flows along path 126. In oneembodiment, the current may be distributed so 50% flows along path 124and 50% flows along path 126. In other embodiments, the ratio may be setto 40% flowing along path 124 and 60% flowing along path 126; 30%flowing along path 124 and 70% flowing along path 126, etc.

During a fault current condition, a fault current higher than the normalcurrent flows into the primary winding 114 and the secondary winding116. When the fault current exceeds a predefined trigger current, theamount of current flowing through the secondary winding 116 is reduced.As such, the amount of amper-turns flowing through the primary winding114 and the secondary winding 116 is no longer equal and the magneticfields within the core 118 will no longer cancel out, thus increasingthe reactance of the first CSD 102. This causes the insertion impedanceof the FCL 101 to increase as a result, thus limiting the fault current.Similar results may be achieved by each of the second CSD 106 and thethird CSD 107.

As will be appreciated, one drawback with conventional fault currentlimiters built as a combined reactor is the build-up of inter-windingvoltage. For example, in the case an exemplary FCL includes a 33 kVlimiter (19.0 kV to earth) with 75% limiting and 5:1 transformer ratioto control the secondary current, the primary winding will see 19.0 kVto earth and drop 14.3 kV when limiting. The secondary winding will alsosee 19 kV to earth when the FCL switching modules are closed, yet 71.5kV (14.3 kV×5) when the switching modules open. In the case the reactorsare insulated separately from earth and the FCL is a mutual reactor, themaximum inter-winding voltage during a solid fault on the load side willbe 14.3 kV+71 kV=85.8 kV. Thus, making an interleaved winding withinsulation levels approaching 85.8 kV where at least 99% of the fluxcancels is a significant engineering challenge.

Generalizing the flux cancellation problem, for a primary winding withvoltage drop V, and a secondary winding with turns ratio 1:w in relationto the primary winding, the voltage developed between windings is amaximum of (1+w)V. If the secondary winding has two FCLMs attachedthereto, the voltage across each module (Vs) can be calculated bysolving the following equation:V=−wV+2Vs.=>(1+w)V/2=Vs.

To address the engineering challenge, embodiments of the presentdisclosure may split FCL 101 into multiple parts or modules, such asfirst, second, and third CSDs 102, 106, 107, and provide the FCLMs 104and 108 interspersed between the windings, as described in greaterdetail above. This allows each CSD to be built with less insulationbetween the primary and secondary windings, and thus makes the task ofcancelling out the flux, and therefore impedance, easier.

More specifically, as shown, the FCL 101 is split into ‘n’ parts (e.g.,‘n’ CSDs), each part including a primary winding with voltage drop V anda secondary winding with turns ratio 1:w in relation to the primarywinding. The voltage developed between windings is thus a maximum of(1+w)V/n. By closing the ends of the reactor arrangement, for example asshown in FIG. 4, the voltages of each FCLM 104, 108 can be calculated asfollows:V=−wV/n+Vs−wV/n+Vs−wV/n=>V=−3wV/n+2Vs

Because n=3 in this example, the voltages can be calculated as follows:V=−wV+2Vs=>(1+w)V/2=Vs.

As a result, the total voltage seen over all modules is (1+w)V. In thiscase, by splitting the reactor into 27 segments, and installing 26switches (e.g., rated at least 3.3 kV each), the inter-winding voltagein the reactor segments will be 1.65 kV, making the insulation needs forFCL 101 much more attainable.

Turning now to FIG. 5, a FCL 201 according to another embodiment of thedisclosure will be described. As shown, in this embodiment, the FCL 201includes multiple FCLMs 256, 258 electrically connected in seriesbetween a secondary winding 216 of a first CSD 202 and a secondarywinding 222 of a second CSD 206. The FCL 201 may further includemultiple FCLMs 260, 262 connected in series between the secondarywinding 222 of the second CSD 206 and a secondary winding 238 of a thirdCSD 207. As arranged, the FCL 201 is split into nx segments, whereinx=the number of FCLMs. The maximum inter-winding stand-off voltage willtherefore be (1+w)×V/n.

Similar to embodiments described above, the first CSD 202 of the FCL 201may include a primary winding 214 and the secondary winding 216 woundaround a first core 218. The second CSD 206 comprises a primary winding220 and the secondary winding 222 wound around a second core 225. TheFCLMs 256 and 258 of the FCL 201 are electrically connected in seriesbetween the secondary winding 216 of the first CSD 202 and the secondarywinding 222 of the second CSD 206. As shown, the primary winding 214 ofthe first CSD 202 is electrically connected in series with the primarywinding 220 of the second CSD 206, for example, along a path 224, andthe primary winding 214 of the first CSD 202 is electrically connectedin parallel with the FCLMs 256 and 258. In some embodiments, the primarywinding 214 and the secondary winding 216 wound around the first core218 may have a same or different number of turns. Similarly, the primarywinding 220 and the secondary winding 222 wound around the second core225 may have a same or different number of turns.

The FCL 201 may further include the third CSD 207 having a primarywinding 236 and the secondary winding 238 wound around a third core 240.The FCLMs 260, 262 are electrically connected in series between thesecondary winding 222 of the second CSD 206 and the secondary winding238 of the third CSD 207. As arranged, FCLMs 256, 258, 260, and 262 areelectrically connected in series along a path 226. Furthermore, theprimary winding 220 of the second CSD 206 is electrically connected inseries with the primary winding 214 of the first CSD 206 and the primarywinding 236 of the third CSD 207, for example, along the path 224. Theprimary winding 220 of the second CSD 206 and the primary winding 236 ofthe third CSD 207 are also electrically connected in parallel with FCLMs256, 258, 260, and 262. Each of the first and second windings of thefirst, second, and third CSDs 202, 206, 207 may be configured to exhibitminimal impedance during a steady state operation, and a comparativelylarger impedance during a fault condition shown in so as to effectivelylimit the fault current.

In summary, various embodiments herein describing FCLMs between windingsof a CSD provide a first advantage including reduced insulation amountsbetween parallel windings of each CSD, and a second advantage includingimproved cancelling of the flux between primary and secondary windingsin the CSDs when the primary and secondary windings are energized.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, the present disclosure has beendescribed herein in the context of a particular implementation in aparticular environment for a particular purpose. Those of ordinary skillin the art will recognize the usefulness is not limited thereto and thepresent disclosure may be beneficially implemented in any number ofenvironments for any number of purposes. Thus, the claims set forthbelow are to be construed in view of the full breadth and spirit of thepresent disclosure as described herein.

What is claimed is:
 1. A fault current limiter comprising: a firstcurrent splitting device comprising a primary winding and secondarywinding wound around a first core; a second current splitting devicecomprising a primary winding and a secondary winding wound around asecond core; and a fault current limiter module electrically connectedin series between the secondary winding of the first current splittingdevice and the secondary winding of the second current splitting device;wherein the primary winding of the first current splitting device iselectrically connected in series with the primary winding of the secondcurrent splitting device.
 2. The fault current limiter of claim 1,further comprising multiple fault current limiter modules electricallyconnected in series between the secondary winding of the first currentsplitting device and the secondary winding of the second currentsplitting device.
 3. The fault current limiter of claim 1, furthercomprising: a third current splitting device comprising a primarywinding and a secondary winding wound around a third core; and a secondfault current limiter module electrically connected in series betweenthe secondary winding of the second current splitting device and thesecondary winding of the third current splitting device.
 4. The faultcurrent limiter of claim 3, wherein the fault current limiter module andthe second fault current limiter module are electrically connected inseries.
 5. The fault current limiter of claim 3, wherein the primarywinding of the second current splitting device is electrically connectedin parallel with the second fault current limiter module.
 6. The faultcurrent limiter of claim 1, wherein the fault current limiter modulecomprises a voltage protection device, a voltage control device, and asolid state switch, and wherein the voltage protection device, thevoltage control device, and the solid state switch are arranged inparallel with one another.
 7. The fault current limiter of claim 1,wherein the primary winding and the secondary winding of the firstcurrent splitting device have a different number of turns, and whereinthe primary winding and the secondary winding of the second currentsplitting device have a different number of turns.
 8. A power systemcomprising: a power source; a load electrically connected to the powersource; a fault current limiter electrically coupled to the power sourceand the load to limit an amount of current during a fault condition, thefault current limiter comprising: a first current splitting devicecomprising a primary winding and secondary winding wound around a firstcore; a second current splitting device comprising a primary winding anda secondary winding wound around a second core; and a fault currentlimiter module electrically connected in series between the secondarywinding of the first current splitting device and the secondary windingof the second current splitting device; wherein the primary winding ofthe first current splitting device is electrically connected in serieswith the primary winding of the second current splitting device.
 9. Thepower system of claim 8, further comprising multiple fault currentlimiter modules electrically connected in series between the secondarywinding of the first current splitting device and the secondary windingof the second current splitting device.
 10. The power system of claim 8,further comprising: a third current splitting device comprising aprimary winding and a secondary winding wound around a third core; and asecond fault current limiter module electrically connected in seriesbetween the secondary winding of the second current splitting device andthe secondary winding of the third current splitting device.
 11. Thepower system of claim 10, wherein the fault current limiter module andthe second fault current limiter module are electrically connected inseries.
 12. The power system of claim 10, wherein the primary winding ofthe second current splitting device is electrically connected inparallel with the second fault current limiter module.
 13. The powersystem of claim 8, wherein the fault current limiter module comprises avoltage protection device, a voltage control device, and a solid stateswitch, and wherein the voltage protection device, the voltage controldevice, and the solid state switch are arranged in parallel with oneanother.
 14. The power system of claim 8, wherein the primary windingand the secondary winding of the first current splitting device have adifferent number of turns, and wherein the primary winding and thesecondary winding of the second current splitting device have adifferent number of turns.
 15. A fault current limiter comprising: afirst current splitting device comprising a primary winding andsecondary winding wound around a first core; a second current splittingdevice comprising a primary winding and a secondary winding wound arounda second core; a first fault current limiter module electricallyconnected in series between the secondary winding of the first currentsplitting device and the secondary winding of the second currentsplitting device; and a second fault current limiter module electricallyconnected in series with the secondary winding of the second currentsplitting device; wherein the primary winding of the first currentsplitting device is electrically connected in series with the primarywinding of the second current splitting device.
 16. The fault currentlimiter of claim 15, further comprising a third current splitting devicecomprising a primary winding and a secondary winding wound around athird core, wherein the second fault current limiter module iselectrically connected in series between the secondary winding of thesecond current splitting device and the secondary winding of the thirdcurrent splitting device.
 17. The fault current limiter of claim 15,wherein the primary winding of the second current splitting device iselectrically connected in parallel with the second fault current limitermodule and the first fault current limiter module.
 18. The fault currentlimiter of claim 15, further comprising a plurality of fault currentlimiter modules electrically connected in series between the secondarywinding of the first current splitting device and the secondary windingof the second current splitting device.